<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8" />
		<title>Document</title>
		<style>
			html{
				font-size: 50px;
			}
			#demo{
				width: 200px;
				height: 200px;
				background: pink;
				font-size: 20px;
			}
			#test{
				width: 2rem;
				height: 2rem;
				background-color: red;
			}
		</style>
	</head>
	<body>
		<div id="demo">
			<div id="test"></div>
		</div>
	</body>
</html>